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7oo

Methods of Ignition.

But one detail has caused some trouble to all inventors, the
question of igniting the explosive mixture without escape of gas.
Three methods have been used:(r) Plame ignition, where a
portion of burning gas is carried through an aperture in the slide
when the latter is just closing. This method has been used
extensively, but occasions frequent misfires when the small aper-
ture becomes carbon coated. (2) Tube ignition, Fig. 682 a.
Here the blind tube A is kept at a white heat by the bunsen
flame c, supplied with gas from B, and whenever the timing valve

E is opened by the spring G, the charge, which has been com
pressed into the ignition chamber D, then ignites. F is the boss
of a lever which keeps valve E on its upper seat, and allows the
contents of the tube to be cleared through hole T. Small engines
have no timing valve, ignition only occurring when the charge is
compressed into the tube. Iron tubes have to be replaced every
fortnight at the latest (3) Electric ignition was adopted in the
Lenoir engine, but in a faulty manner. The current from battery
L was intensified by the coil K. It passed through insulators at
M M, and by platinum points through the cylinder N, the circuit
being closed by the crosshead j, causing sparks at MM, The
covering of the platinum points with carbon or watery vapour